1. Field of the Invention
The present invention relates to a torque converter for a vehicle, and more particularly, to a torque converter for a vehicle, which is improved in an assembling property and structural rigidity and which is designed to restrict movement of a one-way clutch in a direction of a shaft axis and prevent a retainer from being worn.
2. Description of the Related Art
Generally, since a torque converter is designed to transmit power using fluid, it can control the speed acceleration and reduction.
Such a torque converter includes an impeller rotating together with a torque shaft as a single body, a turbine rotating by oil pumped out from the impeller, and a stator improving the torque converting efficiency by directing the oil being returned to the impeller in a rotational direction of the impeller.
Describing in more detail, the stator is designed to direct the oil, which is used to rotate the turbine, toward backsides of blades of the impeller, thereby boosting the rotation of the impeller. Accordingly, a shape of each blade of the stator affects the torque converting efficiency.
When load applied to an engine is increased, the power transmission rate may be deteriorated. In order to prevent this, the torque converter includes a unit for directly connecting the engine to the transmission.
Such a unit is called a lockup clutch that is disposed between a front cover directly connected to the engine and the turbine so that rotation power of the engine can be directly transmitted to the turbine.
As the performance of the engine is improved, the performance of the torque converter should be improved. Generally, the each of the impeller and turbine of the torque converter is comprised of a shell, a core located in the shell, and a plurality of blades disposed between the shell and the core to induce the flow of the oil.
Each of the blades is designed to be relatively thin and coupled to the shell and core through a brazing process.
When the engine is driven, the impeller rotates to direct the oil toward the turbine, thereby rotating the turbine. By the rotation of the turbine, the oil is returned toward the impeller.
At this point, since the flow speed of the oil is very high, the oil pressure acting on the blades is also very high.
Although the blades designed enough to endure the high pressure, it is further required to increase the structural rigidity of the blades as the performance of the engine is enhanced.
However, when the thickness of the blades is increased, a volume of the actuating chamber is reduced by as much as the volume occupied by the increased thickness, thereby deteriorating the converting efficiency.
Furthermore, when the blades increased in the thickness are coupled to the shell and core through the brazing process, the blades may be subject to thermal deformation.
Meanwhile, the stator is disposed between the impeller and the turbine to increase the torque converting rate by converting the flow of the oil.
When an RPM of the impeller is higher than that of the turbine, the stator does not rotate. However, when the RPM of the impeller becomes almost identical to that of the turbine, the oil acts on the backsides of the blades to rotate the stator. At this point, the torque converter functions as a fluid clutch.
By the above-described operation, the stator functions to increase the torque converting rate. At this point, in order to achieve the above-described operation, the stator should be designed to rotate only in a direction.
For the one-way rotation, the stator is installed on an outer race of a one-way clutch having an inner race fixed on a stationary member.
In addition, there is provided a retainer abutting to a sidewall of the one-way clutch to prevent the one-way clutch from moving in a direction of the shaft axis.
That is, the retainer functions to prevent the one-way clutch from moving in the axial direction and to support a side of a needle bearing located between the turbine hub and the one-way clutch.
However, since the retainer is disposed to simply frictional-contacting the needle bearing, when the retainer is worn or moved by force applied in the axial direction, the endurance of the torque converter is deteriorated, reducing the service life thereof.